Re: Linux powerpc new system call instruction and ABI

Excerpts from Dmitry V. Levin's message of May 20, 2021 1:06 pm:

On Thu, May 20, 2021 at 12:40:36PM +1000, Nicholas Piggin wrote:
[...]

quoted

quoted

Looks like struct pt_regs.trap already contains the information that could
be used to tell 'sc' from 'scv': if (pt_regs.trap & ~0xf) == 0x3000, then
it's scv.  Is my reading of arch/powerpc/include/asm/ptrace.h correct?

Hmm, I think it is. Certainly in the kernel regs struct it is, I had in 
my mind that we put it to 0xc00 when populating the user struct for
compatibility, but it seems not. So I guess this would work.

OK, can we state that (pt_regs.trap & ~0xf) == 0x3000 is a part of the scv
ABI, so it's not going to change and could be relied upon by userspace?
Could this be documented in Documentation/powerpc/syscall64-abi.rst,
please?

Yeah I think we can do that. The kernel doesn't care what is put in the
userspace pt_regs.trap too much so if this is your preferred approach
then I will document it in the ABI.

Thanks,
Nick